In practice, components of the type named above are used for example to measure pressure. For this purpose, in the sensor element a pressure-sensitive diaphragm is formed that spans a cavern. As a rule, this cavern is made in the rear side of the sensor element by anisotropic etching; in the case of a silicon sensor element, this is achieved by KOH etching or trench etching. If the component is used for absolute pressure measurement, the cavern is hermetically sealed by the glass carrier so that a defined reference pressure, standardly a vacuum, prevails in the cavern. In this case, the measurement pressure acts only on the front side of the diaphragm. In contrast, components intended for differential pressure acquisition are additionally equipped with a rearward pressure connection in the form of a through-opening in the glass carrier.
In the known component construction, the glass carrier not only seals the cavern, but also acts to reduce mechanical tensions that may result from construction and bonding techniques used during the mounting of the component, e.g. during chip soldering, gluing, etc.
It is known that even the glass-silicon bond of such components is already not free of internal mechanical tensions. These internal tensions arise due to the thermal coefficients of expansion of the silicon and of the glass, which are not matched precisely to each other. Together with the pressure sensitivity, the offset, and thermal influences, this fact is taken into account during an electrical compensation that is carried out after the construction and the electrical connection of the sensor has taken place.
Changes in the mechanical state of tension of the sensor that occur after this compensation result in a drift of the sensor characteristic. In this way, a change in the internal mechanical state of tension has an effect on the diaphragm tension and thus on the deflection of the diaphragm and on its rigidity, resulting in an offset shift and a change in sensitivity. Such a drift of the sensor characteristic is of decisive importance for the precision of the output signal over the entire life span of the component.
After being stored at high temperatures, as well as after storage at high air humidity and increased temperature, such as for example 85° C. and 85% relative humidity, high degrees of drift occur in sensor components that are made of a silicon-glass compound. It is highly probable that this drift is due to a change in the internal mechanical state of tension of the component. This change in the internal mechanical state of tension can be explained by the growth of cracks in the glass. Thus, it is known that microcracks grow at low tension intensities; this is called subcritical crack growth. This crack growth is essentially a function of the air humidity, on mechanical tensions, and on the length of the crack. In the components under consideration here, the exposed glass surfaces, in particular on the lateral walls, mostly have microcracks, which is due to the use of abrasive methods for separating the components. Other surfaces manufactured using abrasive methods, such as for example combined polishing and lapping, also have microcracks.